386 Expeditioii to the 



Mountains. But, at no great distance north of tlits parallel, 

 low ranges of hills begin to appear in the region southwest 

 of lake Michigan, and though too inconsiderable in point of 

 elevation to deserve particular notice, they exhibit peculiar 

 characters, which seem to designate an intimate connexion 

 with the Ozark mountains south of the Missouri. The same 

 succession of strata, the same alternation of crystalline beds 

 with those of mechanical deposition, and similar depositcs 

 of metallic ores are observed here, as in the regions about 

 the Merameg and St. Francis. A marked difference is also, 

 as we think, to be discovered between the rocks and soils on 

 the different sides of this range. Of this we shall speak more 

 particularly in another place. For our present purpose, it is 

 sufficient to assume as a boundary of the region we propose 

 first to consider — a line running from the confluence of the 

 Arkansa and Canadian rivers on the southwest, to the junc- 

 tion of the Mississippi and Wisconsan on the northeast. As- 

 suming this as the direction of the range of the Ozark moun- 

 tains, it will be perceived by examining the map, that to the 

 northwest of this line spreads an extensive plain, reaching to 

 the base of the Rocky Mountains, This plain has been cross- 

 ed in three different places by the exploring party, as already 

 detailed. Once in ascending by the river Platte, between 

 latitude 40° and 41'' 30' — again, in descending the Arkansa 

 in 38°; and thirdly, by the route of the Canadian, in 34°. 

 To the information collected in these journies, we have add- 

 ed a little from other sources, but the greater part of this 

 extensive region yet remains to be explored. 



Sect. I. — Secondary formations connected with the 

 Rocky Mountains. 



I. — Of the great American Desert. 



The portion of country which we design to consider under 

 this division, has an average width of between five and six 

 hundred miles, extending along the base of the Rocky Moun- 

 tains from north to south, as far as we have any acquaintance 

 with that range. Consisting entirely of granitic sands, or of 

 secondary aggregates, into which the detritus of that chain 

 of primitive mountains enters in large proportion — there 

 would be propriety in designating it by some name recogni- 

 ■zing its relation to those mountains. It has been mentioned 

 as the " Mexican Desert,"* a name sufficiently applicable to 

 spme portions of it, but one by no means to be extended to 



" Nuttall's Travels, p. 120. 



